/GR (Enable Run-Time Type Information)

When /GR is on, the compiler defines the _CPPRTTI preprocessor macro. In Visual C++ 2005, /GR is on by default. /GR- disables run-time type information.

Use /GR if your code uses dynamic_cast Operator or typeid. /GR does, however, cause the .rdata sections of your image to increase in size. If your code does not use dynamic_cast or typeid, using /GR- may produce a smaller image.